The invention relates to a seal ring for sealing radially about a shaft and, more particularly, one having an annular sealing lip of a polymeric material one side of which bears resiliently on the shaft with a sealing strip, hydrodynamically-acting backfeed ribs on one side of the sealing strip, an internally cylindrical or conical annular projection on the other side of the sealing strip having and a radial clearance between its cylindrical or conical interior surface and the shaft, the annular projection being united with the sealing strip in a bending-resistant manner, and damming ribs uniformly distributed about and protruding from the interior surface of the annular projection.
A seal ring generally of this type is disclosed in U.S. Pat. No. 3,913,925. It has helical, i.e. hydrodynamically-acting backfeed ribs which make an acute angle with the axis of rotation of the sealed shaft. With the shaft rotating, sealed medium is, therefore, axially returned in the direction of the sealed space. However, before it can leave the seal ring, it has to overcome an end-most sealing strip which, like the helical ribs, bears on the surface of the sealed shaft when the latter is not rotating. The process thus entails lifting both the helical ribs and the sealing strip from the surface of the sealed shaft which achieves wear-free sealing under normal conditions, that is, with the shaft rotating. However, this makes it necessary for the gaps between the helical ribs to be connected with the space containing the sealed medium through bores. Making such bores is technically onerous. It adds to the cost of such seal rings.